trim tab end flange bending

I'm building my trim tab, trying to bend the end flanges that overlap each other and then get riveted together. I've built the wood jig Van's shows (but does not explain) in section 6. It's easy enough to bend over the portion of the flange that is larger (e.g. the leading edge portion of the flange) but where it gets narrow at the aft edge I haven't had much luck. I've tried using the mushroom set to flatten it (like the picture in section 6 shows), but there is so little surface area on the flange at the aft-most edge that I'm simply mashing things up and not really bending that part of the flange over. I've only worked on the bottom flange of one side, so I can cover it with the upper flange, but how do I not make the same mess with the upper flange when I bend it?

To fix the bottom flange I've mangled a little, I'm thinking I may have to grind a little off the aft edge of the bottom flange (that I have not been able to bend so far) so that the upper can fold over it.

The Orndorff video shows just using the hand seamer to make the entire bend. Is that a better way to go? Anybody else had any of these problems and have any suggestions before I mangle the rest of it and have to replace the trim tab skin?

Thanks,
Steve

wood wedge

I made a wood wedge that fit in the trim tab. Clamped it tight in place at the end of the tab & "Wrapped" the flange around it & used the rivet set in the gun to pound it against the block.

Marshall Alexander
RV10 working on wings

I used the hand seamer followed by the wood wedge and plastic mallet for the aft corner area.
Steve
flaps

Another Option

What some folks have done is to cut the skin flaps off and make a small end rib from scrap. That way, you can get the gap between the tab and the elevator just the distance you like with a nice crisp edge.

Here's mine. Click on that pic for a high-res image of it, where you can see more of the detail if you like. I simply used the wood block, clamp, and piece of 1x4 as the bending tool. The end was definitely the toughest, but it went over nicely with the 1x4 and a couple good whacks with the hammer. The elevator tabs are another story. This part may get the 'rib trick' that f1rocket mentioned in the future.

Thanks for the suggestions. I think the problem I had with the first one is that when I clamped the skin in the blocks (my blocks were like Zach's and what Van's describes) and started to bang on it with the flush rivet set, the blocks slid away leaving too much flange exposed. I think maybe by clamping down harder I would have avoided this problem--I used quick clamps rather than some good C-Clamps. Plus, I probably was using too muc pressure in the rivet gun (about 40 psi).

I think I'll try to flatten the original flange back out (as best I can and start over). If that doesn't work, maybe I'll think about the building end ribs like Randy suggests. Anybody who did this have any pictures? I've yet to fabricate anything like a rib--though it seems "simple" enough. Simple being a very relative term, of course.

I'll take another look at it tonight after work. Hopefully I won't need to replace the skin.

Thanks again for the suggestions.

Steve

Steve,
When I built mine at Western PA RV Builders, we used the v-blocks, but also put some double sided tape on the inside block to help hold it in place while banging on it. After the tab was bent, a little laquer thinner helped get the tape out.

Scott F.

Good suggestion re: the double-stick tape, Scott. I'll add that to the process tonight as well. Thanks.

And the only problem with bending it back out is that you might end up with tabs like on my elevator skin... so be careful! I'm pretty sure my crack was from bending back and forth...

Thanks Zach. I worried about bending it back out too--you're picture warned me that could be a problem. Fortunately, flattening and rebending it only once didn't seem to cause a problem (yet). I'll watch it in the future.

To everyone else as well, thanks for the advice. I went back at it last night armed with some heftier C-clams and some double-sided tape and they came out pretty good. The side tabs are a little scratched up (but nothing that some good scotchbrite pad rubbing shouldn't cure) and I might have bent the inboard tabs 1/16-1/8" too much (leaving my trib tab slightly narrower), but they look much better than I anticipated. If for any reason I decide to rebuild a trim tab in the future, I think it will be relatively easy.

One thing I found that works better than using the flush set on the rivet gun directly to the tabs is to use a bucking bar in between--I still hit a bucking bar with the gun, but the various edge shapes of the bucking bar allowed me to direct the force where I really needed it the most. It especially helped to be able to do that down at the trailing edge of the tabs where everything is real narrow.

I also discovered that I can get three, rather than two, foam v-blocks out of the material Van's sends, so I am going to go ahead and insert a third block at a point in the tab where I bent the skin a little too much--that really seems to push the skin back out to where it needs to be and does also seem to make the trim tab a little more solid without adding any weight. Anybody see any problems with doing this?

Thanks again for everyone's suggestion. I can't imagine building this plane without have the resource of a great builders community! I probably would have quit long ago, rather than enjoy it as I have (most days that is).

Steve